--> Abstract: Geochemistry and Microfacies of Lower Aptian Organic-Rich Beds Within the Arcillolitas Abigarradas Member of Paja Formation (Villa de Leiva, Colombia): Its Relationship to Oceanic Anoxic Global Events, by Tatiana Gaona-Narvaez, Florentin J-M.R. Maurrasse, Fernando Etayo-Serna, and Carrie Rebenack; #90124 (2011)

Datapages, Inc.Print this page

AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Geochemistry and Microfacies of Lower Aptian Organic-Rich Beds Within the Arcillolitas Abigarradas Member of Paja Formation (Villa de Leiva, Colombia): Its Relationship to Oceanic Anoxic Global Events

Tatiana Gaona-Narvaez1; Florentin J-M.R. Maurrasse1; Fernando Etayo-Serna2; Carrie Rebenack1

(1) Earth and Environment, Florida Intenational University, Miami, FL.

(2) Instituto Colombiano de Geología y Minería, INGEOMINAS, Bogotá, Colombia.

Detailed analyses of microfacies, inorganic carbon (TIC, wt% CaCO3), organic carbon (TOC, wt% C), and stable carbon isotope measurements (δ13Corg) were carried out in a 68 m Lower Aptian section of the Arcillolitas Abigarradas Member (AAM) of the Paja Formation (Tunja-Villa de Leiva road, Eastern Cordillera of Colombia) to identify the possible link between the organic-rich facies developed in this section and global oceanic anoxic events. The Barremian-Aptian transition is poorly defined, but previous works place it close to the base of the studied section (e.g. Stöhr, 1997). The top of the section coincides with the base of the Upper Aptian Dufrenoyia sanctorum-Stoyanowiceras treffryanus ammonite assemblage zone (Etayo-Serna, 1979).

The Villa de Leiva section includes brown and gray clay-shales, marlstones, and biolithites with very fine gypsum laminae, micritic concretions, and tepee structures; these lithofacies mostly correspond to deposits from supratidal to shallow subtidal environments. It also includes approximately 4 m thick interval of organic-rich clay-shale and marlstones between 191.6 m and 195.5 m from the base of AAM. TOC values in the organic-rich interval range between 1.17% and 5.33% and TIC values range from 9.79 to 44.46%. Horizontal laminations, absence of bioturbation and benthic fossils, as well as increased TOC with the presence of pyritic concretions suggest that the shales were deposited under anoxic conditions in a subtidal hypersaline environment.

Preliminary data from the upper 25 m of the section below the base of the Dufrenoyia sanctorum-Stoyanowiceras treffryanus zone, including the 4 m organic-rich shale interval, show high δ13Corg values from -19.79‰ to -24.65‰. Overall pattern of the δ13Corg curve is in agreement with the upper part of interval C7 and the beginning of interval C8, both of which correlate with the upper part of Tethyan Dufrenoyia furcata ammonite zone. The 4 m organic-rich shale interval in the Villa de Leiva section is therefore subsequent to Oceanic Anoxic Event-1a, which is known to occur in the infrajacent Deshayesites forbesi zone.

References:

Etayo-Serna, F. 1979. Zonation of the Cretaceous of central Colombia by ammonites. Publicaciones Geologicas Especiales del INGEOMINAS, no.2, 186 pp.

Stöhr, D. 1997. Biostratigraphic investigations of the Barremian, Aptian and Early Albian from Villa de Leiva, Colombia. Zentralblatt für Geologie und Paläontologie, Teil I, 1997 (3-6), 559-570.